The present invention is concerned with magnetic flow meters, and particularly, but not exclusively, with magnetic flow meters for the metering of water consumption.
A magnetic flow meter can be used to measure the flow of an electrically conductive fluid along a flow path. The meter is operative to apply a magnetic field across the flow path, on the principle that a conductor moving in a magnetic field causes the induction of a voltage across the conductor. In the case of the fluid flow meter, the conductor in question is the fluid (being water, or an aqueous solution). The direction of the induced voltage is mutually perpendicular to the direction of flow and the direction of the magnetic field.
U.S. Pat. Nos. 3,911,742 and 4,716,769 describe radial field magnetic flow meters. The device described in U.S. Pat. No. 3,911,742 is for use with a catheter tube. As such, it consists of an elongate wand containing a device from which a magnetic field emanates radially. The voltage, or electrostatic field, induced by the flow of water (or other electrically conductive fluid) parallel with the longitudinal axis of the wand, will circulate around the wand. Two electrodes are placed on the surface of the wand, and an electrically insulating septum extending radially from the wand is positioned between the electrodes. The electrostatic field induced about the wand is interrupted by the septum and its magnitude is then measured.
U.S. Pat. No. 4,716,769 describes another meter, which is of similar construction to that described in U.S. Pat. No. 3,911,742, except that it further comprises a body surrounding the wand and septum previously described.
A first aspect of the invention provides a magnetic flow meter including two flow passages, means for applying a magnetic field across both passages, and means for measuring induced voltage in at least one of the passages, including means for shaping the magnetic field applied in use such that the field is substantially perpendicular to the direction of flow and to the direction in which induced voltage is measured.
The invention provides a meter capable of measuring flow with a degree of immunity to asymmetric flow profiles. In that way, flow need not be conditioned upstream of the meter, for example by means of a long stretch of straight piping.
A second aspect of the invention provides a magnetic flow meter including a flow passage, means external of the flow passage for applying a magnetic field across the flow passage, and means for measuring induced voltage in said flow passage, further comprising means within the flow passage for shaping the applied magnetic field in use.
A third aspect of the invention provides a magnetic flow meter comprising a body, a vessel having first and second ends, the vessel defining a flow channel between said ends, and measurement means supported on an anchor of said body for measuring flow within said channel and wherein said anchor extends within said vessel from one or both of said first and second ends.
A fourth aspect of the invention provides a magnetic flow meter including a flow chamber of annular cross-section, and means for defining a magnetic field radially of the flow chamber.
A fifth aspect of the invention provides a magnetic flow meter comprising a flow chamber, means for generating a magnetic field in said chamber and means for measuring voltage induced thereby, wherein the means for generating a magnetic field is at least partially resonant.
A sixth aspect of the invention provides a measurement device including means for receiving an amplitude modulated AC signal and means for converting a signal directly received by the receiving means into a series of coded pulses for digital processing thereof.
In accordance with that sixth aspect, the measurement device preferably comprises means for receiving an amplitude modulated signal representative of an applied magnetic field in a magnetic flow meter and means for receiving an amplitude modulated signal representative of an induced electrostatic field in the magnetic flow meter, and wherein first and second signal conversion means are provided, each being operative to separately directly encode a respective one of said received signals into a stream of coded pulses.
In accordance with that sixth aspect, the measurement device preferably includes analogue to digital conversion means operable to convert an amplitude modulated signal to a digital signal and digital integration means operable to integrate said digital signal.
The digital integration means may include means for rejecting crossover distortion in the output thereof.
A seventh aspect of the invention provides a water meter comprising means defining a water flow channel, means for applying a magnetic field across the channel, and means for measuring a voltage induced in water in said channel in use, wherein said meter includes means for shaping said magnetic field within a volume of the flow channel identified for measurement, such that said field is substantially perpendicular to the direction of induced voltage measured by said measuring means, in use.